Here's how I would do it. Take the distance from the ferrule to the sharkfin, then subtract the distance for the wishbone at the sharkfin (including the part of the wishbone in the rubber). Then subtract the line from the ferrule to the band (including the line in the band). This is the stretched length of the bands. Divide this length by 3.5 and you have the unstretched length. Add back the length of band at each end for covering the line and wishbone, and you have the length to make the band for a 3.5 ratio (25% elongation).
I'm not a typing critique, but 25% elongation won't fly around my house. <img src= " class="smiley" srcset="https://spearfishing.world/forum/images/smilies/emojione/1f606@2x.png 2x" height="23" width="23" loading="eager" data-tooltip="biggrin" aria-label="biggrin">
Who says '' specimen length'' shouldn't count for something...... OK I suck at nerd humor.;)
I like to stretch my rubber Specimen L X 3![]()
Cheers, Don